This invention relates generally to acceleration protective suits for pilots, and more particularly to an improved valve for controlling pressurization of such anti-G suits.
The current generation of fighter/attack aircraft has aerodynamic, structural, and propulsion systems tailored for high energy maneuvering. This high energy maneuvering capability provides the pilot with the tactical advantage required to maintain air superiority but challenges his ability to fully use this capability because of the high accelerative forces associated with it. These forces effectively increase the weight of the pilot's blood which is equivalent to lengthening his cardiac cerebral hydrostatic column; this places a heavy burden on his heart as it attempts to overcome the weight of this column and supply oxygenated blood to the brain. Failure of the heart to perform this function causes the pilot to experience a loss of vision, a failure of cognitive processing, and eventually a loss of consciousness.
To increase the pilot's ability to withstand these accelerative forces, he is provided with an anti-G suit containing bladders which inflate under control of an anti-G valve and applies pressure over the abdominal and leg areas. Further protection is provided if the pilot performs a straining maneuver in combination with the suit pressurization. Critical to the amount of protection provided by these actions, however, is the time at which they occur relative to the G profile. If the suit is pressurized too early, the pilot may experience pain and discomfort which may inhibit his straining maneuver. If it is pressurized too late, blood pooling in the lower extremities may have already occurred and created a condition which the eventual suit pressurization may not be able to overcome. Ideally, the suit should be pressurized in synchrony with the increasing G profile.
The standard anti-G valve with the widest current use has had no basic improvements since it was developed during World War II. This valve is basically a spring loaded mass system which controls the anti-G suit pressure by the action of an applied G-force which opens and closes the valve by displacing the mass. The opening of the valve is directly proportional to the amount by which the longitudinal component of the G-force exceeds a preset threshold.
This open-loop proportional method of control introduces an inherent lag between the applied G-force and the suit pressure which is particularly noticeable during high rates of G onset, a common occurrence in modern high performance aircraft. Consequently, the pilot may be left with the task of combatting high G-forces without assistance from his suit, thereby reducing his tolerance to G-forces, adding to his stress and fatigue, and diminishing his mission effectiveness.
A modified version of the standard anti-G valve has been developed which achieves an increase in the rate of G-suit pressurization. Two concepts are utilized to accomplish this objective: (a) the suit is prepressurized to a nominal pressure, and (b) the port size of the valve is increased thereby increasing the pressurizing air volume through the valve.
There are, however, some disadvantages to this modified valve. For example, suit prepressurization can be uncomfortable for pilots for long periods of time and will require provisions for being switched on and off. Also, the increase in air flow capacity is limited to the maximum capacity of the standard G-valve design. Furthermore, the basic problems associated with the standard valve, previously discussed, still remain.
Finally, it would be very advantageous to be able to study a pilot's physiological response to G-stress under various conditions of G-suit pressurization. This is virtually impossible with the standard valve, since it only has one possible mode of operation. A valve which can be adapted to respond to different parameters would not only provide greater flexibility in research, but also provide greater effectiveness and comfort for the pilot.